This invention relates to a system for applying a liquid mist and, in particular to a system for applying a mist of dampening fluid in lithographic printing.
Dampening fluids are utilized in lithographic printing to cover areas of the printing plate which are not treated by ink. These dampening fluids are generally water based liquid solutions which contain various additives and are well known in the art. The prior art discloses numerous systems for applying the dampening fluid in the form of a spray or mist to the free surface of either the printing plate or transfer rollers in the roller train which supplies the ink mixture to the printing plate. Among such systems is that disclosed in U.S. Pat. No. 4,232,603 to Suvak et al which discloses the use of a pickup roll having a loop, mesh or bristled surface partially immersed in a dampening fluid fountain. An air nozzle blows air over the surface of the pickup roll to create a mist which is directed toward a roll in the printing train.
Several U.S. patents disclose the use of brush-type rollers which pick up dampening fluid either directly from a fountain or from another roller, and which utilize deflector or "flicker" means to bend and snap the bristles to eject a fine mist of the dampening fluid. Among such systems are U.S. Pat. Nos. 2,853,004; 3,257,940; 3,545,379; 4,143,596; 4,619,198; and 4,787,314. However, systems which immerse the brush roller directly into the dampening solution or which use a smooth surfaced intermediate roll between the dampening solution and the brush roller have difficulties in controlling the mist that is generated. Other difficulties in such systems arise from the structural placement of the components of the mist application system, as well as the location on the roller drive train on which the mist is applied.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved dampening fluid application system for use in lithographic printing systems.
It is another object of the present invention to provide a dampening fluid mist application system in which the mist can be more precisely controlled as to amount, drop size and direction.
It is a further object of the present invention to provide a dampening fluid mist application system in which the mist is applied in an optimum location on the train of rollers in a lithographic printing system.
It is yet another object of the present invention to provide a dampening fluid mist application system which can be easily adapted to new printing systems or retrofitted into existing printing systems.